A technique is known for dynamically extending a storage area provided to an external apparatus, such as a host computer. For example, a so-called “thin provisioning” technique is described in Japanese Patent Application Laid-Open Publication No. 2003-15915.
According to the thin provisioning technique described in Japanese Patent Application Laid-Open Publication No. 2003-15915, a host computer is provided with a virtual volume that is a virtual storage area of a storage apparatus communicatively coupled to the host computer. In addition, the storage apparatus has a pool area prepared thereto. The pool area is a group of logical devices that are logical storage areas (hereinafter “LDEV” or “logical volume”), and each LDEV is configured with a multiplicity of logical blocks (hereinafter “block”) that are unit storage areas.
When receiving a data write request from the host computer, the storage apparatus allocates an unallocated block among blocks included in the pool area to a virtual volume.
The above storage apparatus may be configured so that a plurality of virtual volumes share the same pool area. In this case, each of the plurality of blocks belonging to the same pool area is allocated to a different virtual volume, respectively.
A need to keep data stored in the storage apparatus in an encrypted state may arise from the viewpoint of data security. For example, Japanese Patent Application Laid-Open Publication No. 2005-303981 discloses a storage apparatus that has a function of encrypting to-be-stored data to ensure the security of data stored in the storage apparatus.